Method and apparatus for rapid assignment of a traffic channel in digital cellular communication systems

ABSTRACT

A method and apparatus for rapidly assigning traffic channels to a plurality of mobile stations in a wide area high-speed packet data cellular communication system. Mobile stations transmit access probes on randomly selected access channels to selected base stations to initiate traffic channel assignments. The access probe comprises a pilot preamble, a traffic channel request, and a pilot/data request channel (DRC). The pilot preamble allows the selected base station to easily detect the access probe transmission. The traffic channel request includes data that identifies the mobile station. Immediately after transmitting the traffic channel request, the mobile station begins communicating with the base station on both the forward and reverse communication links. The selected base station immediately supervises the mobile station&#39;s transmission power. The mobile station selects from a group of available power control sub-channels. The mobile station selects an available channel and an associated power control sub-channel from the list.

CLAIM OF PRIORITY UNDER 35 U.S.C. §120

The present Application for Patent is a Continuation and claims priorityto patent application Ser. No. 10/007,206 entitled “Method and Apparatusfor Rapid Assignment of a Traffic Channel in Digital CellularCommunication Systems” filed Nov. 9, 2001, now U.S. Pat. No. 6,741,861now allowed, which is a Continuation of patent application Ser. No.09/158,697 entitled “Method and Apparatus for Rapid Assignment of aTraffic Channel in Digital Cellular Communication Systems” filed Sep.22, 1998, now issued as U.S. Pat. No. 6,366,779 and assigned to theassignee hereof and hereby expressly incorporated by reference herein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to digital wireless communication systems, andmore particularly to methods for rapidly assigning traffic channels indigital wireless communications rapidly assigning traffic channels indigital wireless communications systems.

2. Description of Related Art

Wireless communication systems facilitate two-way communication betweena plurality of subscriber mobile radio stations or “mobile stations” anda fixed network infrastructure. Typically, the mobile stationscommunicate with the fixed network infrastructure via a plurality offixed base stations. Exemplary systems include such mobile cellulartelephone systems as Time Division Multiple Access (TDMA), Code DivisionMultiple Access (CDMA) systems, and Frequency Division Multiple Access(FDMA) systems. The objective of these digital wireless communicationsystems is to provide communication channels on demand between themobile stations and the base stations in order to connect the mobilestation users with the fixed network infrastructure (usually awired-line system).

Mobile stations typically communicate with base stations using aduplexing scheme that allows for the exchange of information in bothdirections of connection. In CDMA communication systems, transmissionsfrom a base station to a mobile station are referred to as “forwardlink” transmissions. Transmissions from a mobile station to a basestation are referred to as “reverse link” transmissions. The basic radiosystem parameters and call processing procedures for exemplary prior artCDMA systems is described by the TIA specification which is entitled“Mobile Station-Base Station Compatibility Standard for Dual-ModeWideband Spread Spectrum Cellular System,” TIA/EIA/IS-95-A, published inMay 1995 by the Telecommunications Industry Association, and referred tohereafter as “IS-95”.

Both voice and data services are available using CDMA communicationsystems made in accordance with IS-95. However, disadvantageously, datacalls use the same airlink protocols, traffic channels, physical layers,signaling methods, call processing schemes and airlink protocols as usedby the voice calls. While the prior art call processing schemes andsignaling methods are efficient and effective for voice services, theyare inefficient for data services, especially when the data servicescomprise very short duration calls. As described in more detail below,it can take between two and three seconds to establish or “setup” anaverage voice traffic channel using the prior art call processingschemes. While this setup time may be acceptable for a voice call that,on the average, may have a duration of between 100 and 300 seconds, itis unacceptable for a data call having a duration of only a few seconds,or less. Therefore, an improved technique is needed for assigning datatraffic channels in a CDMA communication system. The causes of trafficchannel assignment delays in the prior art systems become apparent byreviewing CDMA call flow examples. Therefore typical prior art CDMA callflow examples are now described.

CDMA Call Flow Examples

Table 1 shows a simple call flow example as set forth in IS-95. Table 1uses the following conventions:

-   -   All messages are received without error.    -   Receipt of messages is not shown (except in the handoff        examples).    -   Acknowledgements are not shown.    -   Optional authentication procedures are not shown.    -   Optional private long code transitions are not shown.

TABLE 1 Simple Call Flow Example - Mobile Station Origination MobileStation Base Station Detects user-initiated call Sends OriginationMessage > Access Channel > Sets up Traffic Channel Begins sending nullTraffic Channel data Sets up Traffic Channel < Paging Channel < SendsChannel Assignment Message Receives N_(5m) consecutive valid framesBegins sending the Traffic Acquires the Reverse Traffic Channel preambleChannel Begins transmitting null Traffic < Forward Traffic < Sends BaseStation Channel data Channel Acknowledgement Order Begins processingprimary traffic < Forward Traffic < Sends Service Option in accordancewith Service Channel Response Order Option 1 Optional Optional SendsOrigination Continuation > Reverse Traffic > Message Channel OptionalOptional Applies ring back in audio path < Forward Traffic < Sends AlertWith Information Channel Message (ring back tone) Optional OptionalRemoves ring back from < Forward Traffic < Sends Alert With Informationaudio path Channel Message (tones off) (User conversation) (Userconversation)

Table 1 shows a simple call flow example wherein a mobile stationoriginates a call. Base station originated calls follow similarprocedures. Messages are transmitted from the mobile station to the basestation using the access channel. Messages are transmitted from the basestation to the mobile station using the paging channel. As shown inTable 1, the mobile station first detects a user-initiated call, andthen sends an “origination” message via the CDMA access channel. Theaccess channel is a slotted random access channel. The mobile stationtransmits on the access channel using a random access procedure. Manyparameters of the random access procedure are supplied by the basestation in an access parameters message. The entire process oftransmitting one message and receiving (or failing to receive) anacknowledgement for that message is called an “access attempt.” Eachtransmission in the access attempt is called an “access probe.” Withinan access attempt, access probes are grouped into access probesequences. Each access probe sequence comprises a fixed number of accessprobes. The first access probe of each access probe sequence istransmitted at a specified power level relative to the nominal open looppower level. Each subsequent access probe is transmitted at a powerlevel that is a specified amount higher than the previous access probe.

In normal CDMA operation, when a mobile station user initiates a phonecall, the mobile station sends an access probe to the base station. Ifthe access probe is properly received by the base station, the mobilestation should receive back an acknowledgement from the base station.Once the acknowledgement is received by the mobile station, the mobilestation is instructed by the base station to wait and to stop sendingfurther access probes to the base station. This is necessary becauseaccess probes produce interference on the communication channel. Themobile station therefore waits until it is assigned a traffic channel bythe base station. The base station then communicates this request for atraffic channel and information about the mobile station to a basestation controller (BSC). The BSC performs several administrativefunctions, possibly including authenticating the mobile station. The BSCthen reviews the pool of available resources and allocates an elementfor the requesting mobile station.

As shown in Table 1, the base station informs the mobile station of thetraffic channel assignment by sending a channel assignment message viathe paging channel. Once the mobile station receives its channelassignment from the base station, it changes its receive and transmitfrequencies, in addition to other relevant parameters, to the assignedtraffic channel. The mobile station then attempts to initiatecommunication on the assigned traffic channel by establishing or“setting up” the traffic channel. if the traffic channel initializationis successful, the mobile station then acquires the traffic channel. Themobile station then begins sending a preamble on the reverse trafficchannel to allow the base station to acquire the mobile station. Asshown in Table 1, the base station acquires the reverse traffic channeland sends a base station acknowledgement order to the mobile station ifthe reverse traffic channel was properly acquired. At this point themobile station and the base station begin negotiating service. Thecommunication link can fail at any point during this negotiationprocess. However, if the negotiation process is successful,communication commences and a telephone conversation ensues. if themobile station receives pilots from more than one base station, it maythen request the allocation of additional traffic channels from theother base stations.

The prior art traffic channel assignment procedures shown in Table 1take a relatively long period of time to execute. For example, from thetime a base station receives a traffic channel request from a mobilestation via the access channel, it typically takes between two and threeseconds before a traffic channel is assigned and a base stationacknowledgment order is transmitted to the mobile station. As notedabove, this service delay is acceptable for voice services wherein theduration of voice calls are typically between 100 and 300 seconds.However, this service delay is unacceptable for data services whereinthe duration of data calls are typically only a few seconds, or less. Inaddition, the assignment of traffic channels utilizes scarce systemresources such as specific base station hardware, limited numbers ofcode channels, and transmission bandwidth (which is required both fortracking and for power control even when no data is transmitted).Therefore, to improve system capacity and throughput, it is advantageousto rapidly de-assign traffic channels whenever the user terminal goesdormant. That is, whenever the user terminal and the base station nolonger have information to exchange, it is desirable to rapidlyde-assign the traffic channel associated with the mobile station and toquickly re-assign the traffic channel when more data is presented fortransmission.

In addition to delaying service to the user (whether the service bevoice or data based), delays associated with the assignment of trafficchannels create further delays in providing power control of the userterminal (typically a cellular telephone). Because the user terminal'stransmission power can vary greatly, it is important to control thepower of the user terminal as quickly as possible to avoid unnecessaryco-channel interference that can both reduce system capacity and resultin loss of the traffic channel. Therefore, it is desirable to bothreduce the delays associated with the assignment of traffic channels andsupervise the user terminals as quickly as possible. The presentinvention provides a method and apparatus that address these needs byrapidly assigning traffic channels to mobile stations in a wirelesscommunication system. The present invention also provides a mechanismfor rapidly and efficiently controlling the transmission power of therequesting mobile stations.

SUMMARY OF THE INVENTION

The present invention is a novel method and apparatus for rapidlyassigning traffic channels in a wireless high-speed packet datacommunication system. The method and apparatus uses an access probecomprising a pilot preamble, a traffic channel request, and a pilot/datarequest channel (DRC) field. The access probe is transmitted to aselected base station via a reverse link access channel whenever amobile station initiates a traffic channel assignment request. Themobile stations randomly select the access channels. The access probe ismasked using a long code cover equal to an access channel cover code.All mobile stations use the same access channel cover when transmittingon a selected access channel. The mobile station transmits a sequence ofaccess probes of increasing power until the access attempt is eithersuccessful or terminates. The mobile station monitors the forward linkcontrol channel and the forward link traffic channel while it istransmitting access probes to the base station.

The pilot preamble of the access probe allows the selected base stationto easily detect the access probe transmission. In accordance with thepresent inventive method and apparatus, the mobile station transmits thetraffic channel request immediately following the transmission of thepilot preamble. The traffic channel request includes data thatidentifies the requesting mobile station to the base station. Typically,this identifying data comprises an MSI that was previously assigned tothe mobile station when it registered with the wireless packet datasystem. In addition to transmitting its MSI, the mobile station alsotransmits data that identifies the signal strengths and identities ofall other base stations having received signal strengths exceeding apre-determined threshold. Immediately after the mobile station transmitsthe traffic channel request it can begin using the reverse link trafficchannel to transmit useful data to the selected base station. In oneembodiment, the mobile station transmits the pilot/DRC field to the bestbase station it receives (i.e., the base station with the strongestsignal received by the mobile station). The DRC includes traffic channeldata rate information and is used by the mobile station to request themaximum data rate that it can reliably demodulate. The mobile stationcontinues to transmit the pilot/DRC field for a period defined by theaccess probe tail.

Rather than waiting for the base station to authenticate and to assign atraffic channel to the mobile station, the mobile station beginscommunication on the traffic channel (identified by its MSI) immediatelyafter transmission of the access probe. In essence, the traffic channelsare pre-assigned to the mobile stations. In addition to speeding theassignment of traffic channels in a wireless packet data communicationsystem, the present method and apparatus also allows base stations tobegin supervising the transmission power levels of the mobile stationimmediately after the transmission of the access probe. In oneembodiment, the mobile stations select from a group of available powercontrol sub-channels. The mobile station uses the selected power controlsub-channel when it begins to transmit data on the reverse communicationlink. The base station subsequently associates the mobile's MSI with theselected power control sub-channel. The mobile station thereaftermonitors the forward channel and determines whether its MSI isassociated with the power control sub-channel it previously selected.

By enabling fast power level supervision by the base station, thepotential interference that could have been caused by a rogue oruncontrolled mobile station is drastically reduced. In addition, byspeeding the traffic channel assignment process, the present inventivemethod and apparatus facilitates short duration data calls, increasessystem capacity and throughput, and reduces the system costs associatedwith dormant mobile stations. Another embodiment of the presentinvention reduces the randomness of the channel selection process andthereby reduces the chance of collisions. In accordance with thisalternative embodiment, the base station advertises the identities ofavailable traffic channels (and available power control sub-channels)via the forward link control channel. In accordance with thisembodiment, rather than randomly selecting a traffic channel based onits MSI, the mobile station selects an available channel (and associatedpower control sub-channel) from the available channel list advertised bythe base station. After selecting the available channel and powercontrol sub-channel, the mobile station initiates the channel assignmentprocess using the access probe described in the first embodiment.Another alternative embodiment is described wherein the base station,and not the mobile station, initiates a traffic channel request. Thisembodiment is used when the base station has data identified for aselected mobile station. In accordance with this embodiment, whenever abase station has data identified for a particular mobile station that iscurrently not connected to the base station, a base station controllerdirects all base stations within the selected mobile station's pagingradius to transmit “page” messages to the mobile station over theforward link. The base stations use the mobile station's MSI to identifythe page messages as directed to a particular mobile station. The mobilestation continuously monitors the control channel and responds to pagesaddressed to its associated MSI. When the mobile station detects pagesaddressed to it (i.e., pages containing its MSI), it uses one of themethods described above to complete the traffic channel assignmentprocess.

In yet another alternative embodiment, the base station initiates atraffic channel assignment by advertising both the identity of theselected mobile station and an associated power control sub-channel overthe forward link control channel. The mobile station continuouslymonitors the forward link control channel and detects pages containingits associated MSI. When the mobile station identifies its page ittransmits a traffic channel request message as described above. However,the mobile station also immediately begins monitoring the power controlsub-channel identified in the page message.

The details of the preferred and alternative embodiments of the presentinvention are set forth in the accompanying drawings and the descriptionbelow. Once the details of the invention are known, numerous additionalinnovations and changes will become obvious to one skilled in the art.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of an exemplary wireless packet datacommunication system adapted for use with the present invention.

FIG. 2 shows an example of an access probe used to practice the rapidtraffic channel assignment method and apparatus of the presentinvention.

Like reference numbers and designations in the various drawings indicatelike elements.

DETAILED DESCRIPTION OF THE INVENTION

Throughout this description, the preferred embodiment and examples shownshould be considered as exemplars, rather than as limitations on thepresent invention.

An Exemplary Wide-Area High-Speed Packet Data Communication SystemAdapted to Use the Present Rapid Traffic Channel Assignment Method andApparatus

The present inventive method and apparatus is intended for use in ahigh-speed cellular/Personal Communication System (PCS) CDMA system thatprovides wide-area high-speed packet data connectivity for both fixedand mobile terminals. A block diagram of such an exemplary packet datacommunication system is shown in FIG. 1. As shown in FIG. 1, thecellular/PCS packet data communication system 100 includes at least onemobile station 102, at least one base station 104, and an interface withsome type of data router, shown in FIG. 1 as Internet Protocol (IP)router 106. The mobile stations 102 typically include a terminalequipment (TE) block 108 and a mobile termination (MT) block 110. The TEblock 108 comprises a device that provides an interface to a humanoperator. Typically, the TE 108 comprises a laptop computing device,personal digital assistant (PDA), handheld computing device, or thelike. The MT block 110 comprises a modulator/demodulator (modem) capableof modulating (and demodulating) data into radio-frequency signalscompatible with the air interface used by the cellular/PCS CDMA system100. The MT block 110 is typically implemented using a PCMCIA compatiblecard, an external modem, or a module within the TE block 108.

As shown in FIG. 1, the mobile station 102 communicates with the basestation 104 via an air interface or airlink 112. The base station 104typically comprises at least one network access point or base stationtransceiver subsystem (BTS) 114 with a transceiver 160 and at least oneradio link protocol (RLP) and signaling manager (RSM) 116. The BTS 114provides the communication interface between the plurality of radiofrequency (RF) mobile stations 102 and a fixed (typically wired) datacommunications network. The RSM 116 performs signaling and radio linkprotocol management functions. In addition, the RSM maps user addressesprovided by a data router (for example, as shown in FIG. 1, the IProuter 106) to mobile station identifiers, and vice versa. Some systemsinclude only one RSM 116 per base station 104; others may include an RSM116 for each BTS 114. A more detailed description of the operation andfunctions performed by the mobile station 102, the base station 104, andthe IP router 106 is beyond the scope of the present invention.

The packet data communication system 100 uses additional and separate RFchannels channel (i.e., different RF channels) from those used by theexisting IS-95 systems. The RF channels support the transmission ofpacket data transmissions over the airlink 112 between the plurality ofmobile stations 102 and the plurality of base stations 104. The trafficchannels typically include a power control sub-channel (Pi) and achannel identifier (Wi). The channel identifiers are used to identifytransmissions originating from and destined to a mobile station i. Allbase stations 104 in the packet data communication system 100 preferablytransmit pilot, control channel and reverse link power controlinformation to the mobile stations 102 in a burst-continuous manner. Thebase stations 104 preferably use the control channels to broadcast or“advertise” system-wide parameters to the mobile stations 102. Inaddition, the control channels can be used to provide data to mobilestations that have not yet been assigned traffic channels, or as analternative to using the traffic channel for data communications. Themobile stations 102 continuously monitor the forward link controlchannels.

The packet data communication system 100 of FIG. 1 may optionally bedeployed in conjunction with or independently from an existing IS-95compliant CDMA communication system. When deployed independently fromexisting IS-95 systems (or when deployed in a location where no IS-95systems exist), the system 100 has no interaction with the underlyingvoice services provided by the IS-95 systems. In contrast, when deployedin conjunction with an existing IS-95 system, the control channels carryinformation related to the IS-95 system to support handoffs from thesystem 100 to the IS-95 system. In addition, the information carried onthe system 100 control channels facilitates the exchange of informationbetween the IS-95 system and the packet data communication system 100 ofFIG. 1. For example, in addition to other messages, the delivery ofmobile-terminated short message services (SMS) and call deliverynotifications from the IS-95 system to the system 100 of FIG. 1 are alsosupported.

The system 100 forward links differ from the IS-95 forward links in someimportant respects. For example, the system 100 forward links areentirely dedicated to a single mobile station 102 at any given instantin time. That is, at any given instant in time, a base station 104 ispermitted to transmit on the forward channel to a mobile station 102 ina one-to-one communication link thereby providing the mobile station allof the available forward link capacity. In contrast, in an IS-95 system,base stations may transmit to multiple mobile stations, and a mobilestation may receive transmissions from more than one base station. Inthe system 100, the transmission rate used on the forward linkcorresponds to the transmission rate requested by the mobile station onthe reverse link.

The pilot channels transmitted by the base stations 104 over the forwardlinks of system 100 also differ from those transmitted over the IS-95forward links. In IS-95 communication systems, base stationscontinuously transmit a pilot channel comprising an unmodulated,direct-sequence spread spectrum signal. The IS-95 pilot channel allowsmobile stations to acquire the timing of the forward channel, provides aphase reference for coherent demodulation, and provides a means forsignal strength comparisons between base stations for determining whento perform a handoff operation. In contrast, the pilot channel used inthe system 100 comprises a burst transmission embedded in the forwardlink traffic stream. The mobile stations 102 continuously monitor andmeasure the relative strengths of the pilot channels transmitted by thebase stations 104.

Mobile stations preferably register with the base station that istransmitting the strongest pilot channel signal. After powering on, orafter entering a new cell area, the mobile station 102 sends aregistration message to the base station 104 that is transmitting thestrongest pilot signal to the mobile station 102. The mobile station 102identifies itself using a randomly generated identification number inthe first registration message that it sends to the base station 104.The base station 104 assigns the mobile station a system-generatedmobile station identifier (MSI) when it receives the registrationmessage from the mobile station 102. The base station 104 then transmitsthe MSI to the mobile station 102 in an MSI assignment message via theforward link control channel. Both the base station and mobile stationuse the MSI to identify the mobile station in any subsequent messages(including traffic channel requests).

In one embodiment of the present method and apparatus, mobile stationsinitiate communication with base stations by transmitting access probesto the base stations using access channels in the reverse communicationlink of the airlink 112. The mobile stations randomly select an accesschannel when requesting a traffic channel assignment from a basestation. Because the mobile stations use random access transmissions onthe access channels, the access channels preferably support mechanismsfor collision detection and resolution. The mobile stations use theaccess channels to transmit traffic channel requests to a selected basestation. In addition to facilitating traffic channel requests, theaccess channels are also used during the registration process totransmit registration messages from the mobile stations to selected basestations. The access channels may also be used to carry short messages.

Mobile Station Initiated Traffic Channel Assignment

In one embodiment of the present method and apparatus, a mobile stationrequests the assignment of a data traffic channel from a selected basestation by transmitting access probes of increasing power until theaccess attempt is either successful or the access attempt terminates. Inaccordance with the present method and apparatus, the mobile stationtransmits a sequence of access probes having the format shown in FIG. 2.Each probe 200 in a sequence is transmitted at increased power levelsuntil either the message contained in the probe is acknowledged or thesequence elapses. The mobile station typically monitors the forward linkcontrol channel and the forward link traffic channel (in cases where themobile station has already been assigned an MSI) while it istransmitting access probes on the access channel.

As shown in FIG. 2, the access probe 200 comprises a pilot preamble 202,a traffic channel request 204, and a pilot/data request channel (DRC)field or “probe tail” 206. A long code cover 208 is used to cover ormask the mobile station's transmissions. The long code cover preferablycomprises an access channel cover 210 and a mobile station identifier(MSI) cover 212. The long code cover 208 determines the communicationchannel used by the mobile station at any given instant in time. Forexample, the mobile station transmits on the access channel when it usesthe access channel cover 210 to cover its transmissions. Similarly, themobile station transmits on the traffic channel identified by its MSIwhen it uses the MSI cover 212 to cover its transmissions. Note that allmobile stations use the same access channel cover 210 when transmittingon a selected access channel.

The pilot preamble 202 allows the selected base station to easily detectthe access probe transmission. The pilot is a known sequence of datathat can be readily detected by the base station. In one mode ofoperation, when the mobile station is connected to the base station andtransmitting data (i.e., when the mobile station is in a “connected”state), the mobile station continuously transmits the pilot channel tothe base station. In this state, the base station uses the pilot channelto track the mobile station and control its power transmissions. Inaddition, the base station uses the pilot channel as a phase referenceto coherently demodulate data that is transmitted by the mobile station.

In accordance with the present method and apparatus, immediatelyfollowing transmission of the pilot preamble 202, the mobile stationtransmits the traffic channel request message 204. The traffic channelrequest 204 includes data that identifies the mobile station to the basestation. When requesting a traffic channel, the mobile station shouldpreviously have been assigned an MSI by the base station (as a result ofa previous registration operation) and therefore, the mobile stationpreferably includes its MSI as a part of the traffic channel request204. If an MSI was not previously obtained, the mobile station shouldfirst register with the base station before initiating a traffic channelrequest. During the registration process, the mobile station uses arandomly generated number instead of the MSI. After obtaining an MSIfrom the base station, the mobile station uses the MSI to identifyitself during subsequent transmissions.

In addition to transmitting its identifier, the mobile station alsotransmits data (in the traffic channel request 204) that identifies thesignal strengths and identities of all other base stations havingreceived signal strengths exceeding a pre-determined threshold.

In one embodiment of the present invention, the traffic channel requestincludes a transaction identifier, a reference pilot, a pilot strengthindicator, and a timer status field. The transaction identifieridentifies each transaction between the requesting mobile station andthe selected base station. The mobile station sets the transactionidentifier to a selected number and uses this number in other messagesassociated with the transaction. The reference pilot is set by themobile station to the pseudo-noise (PN) sequence offset of the pilotchannel used by the mobile station to derive its time reference (thereference pilot), relative to a zero offset pilot PN sequence. The pilotstrength indicator is set by the mobile station to a computed value thatis based upon the strength of the pilot channel received from the basestation. In one embodiment, this strength estimate is computed as thesum of the ratios of received pilot energy per“chip”(“Ec”) to the totalreceived spectral density (“Io”) (signal and noise energy), for at mostk multi-path components (where k is the maximum number of multi-pathcomponents that can be concurrently demodulated by the mobile station).The timer status field is set by the mobile station and indicateswhether a pilot drop timer corresponding to the pilot channel hasexpired.

In accordance with the present inventive method and apparatus,immediately after transmitting the traffic channel request 204, themobile station can begin using the reverse link traffic channel, definedby Wi (i.e., identified by its MSI), to transmit what is effectivelyreverse link traffic data to the base station. The mobile stationtransmits the probe tail 206 on the reverse link traffic channelidentified by its MSI. The probe tail 206 comprises pilot channelinformation and data request channel (DRC) information. The mobilestation preferably transmits its DRC to the “best” base station it canreceive (i.e., the base station having the strongest signal received bythe mobile station). The mobile station uses the DRC to request a datachannel that has the maximum data rate that the mobile station canreliably demodulate. The mobile station must transmit the pilot/DRCchannel to allow the selected base station to track it and to controlthe mobile station's transmission power. The mobile station continues totransmit the pilot/DRC channel for a time period defined by the probetail 206. This time period is a parameter that is advertised by the basestation on the forward link control channel.

Advantageously, the mobile station need not wait to receive a trafficchannel assignment, as it must do in the prior art CDMA systemsdescribed above. Rather, in accordance with the present inventive methodand apparatus, immediately after transmitting its access probe 200, themobile station begins using the reverse link traffic channel identifiedby its MSI. The mobile station immediately begins transmitting pilot andDRC information on the reverse link. In addition, the mobile station canimmediately begin obtaining data via the forward link without waitingfor the base station to authenticate and acknowledge the traffic channelrequest as is required by the prior art call processing methods. Inessence, the traffic channels are “pre-assigned” using the presentmethod and apparatus.

When the base station receives the access probe 200, it transmits atraffic channel assignment message on the forward link traffic channelat the data rate defined in the DRC message previously transmitted bythe mobile station. The base station can complete the assignment oftraffic channels for all base stations requested by the mobile station(including the assignment of all necessary resources) beforetransmitting the first traffic channel assignment to the mobile station.Alternatively, and especially in cases when the traffic channelassignment process would require exceeding the period defined by theprobe tail 206, the base station can transmit a first traffic channelassignment to the mobile station thereby assigning it the power controlsub-channel used by the accessed base station. Subsequently, the basestation can complete the traffic channel assignment process bytransmitting additional traffic channel assignment messages once theresource allocation process is complete. The only additional parameterthat is required to complete the traffic channel assignment process isthe identity of the power control sub-channel.

In one embodiment, the base station specifies in the traffic channelassignment message the parameters of all of the traffic channelsassigned to serve a specified mobile station. For example, in oneembodiment, the traffic channel assignment message includes atransaction identifier, a channel record (comprising a thirty-two bitnumber to identify the channel assigned to the mobile station), one ormore occurrences of a pilot pseudo-random noise (“PilotPN”) field, and apower control bit field. The transaction identifier identifies eachtransaction between the mobile station and the base station. The basestation sets the transaction identifier to a selected number and usesthis number in other messages associated with the transaction (e.g.,traffic channel request messages and registration messages). The channelrecord includes both a system channel RF frequency to be used by themobile station and a related CDMA system type. The pilotPN fieldcontains the PN offset of the base station that the mobile station willcommunicate with in order to exchange subsequent traffic channeltransmissions. The base station associated with the PN offset willtransmit a power control bit to the mobile station during subsequenttraffic data exchanges. In addition, the mobile station uses the pilotPNfield to identify the base station that it is allowed to transmit itsDRC channel to. This field also informs the mobile station of thecontrol channel and forward traffic channel that the mobile station willmonitor. The power control bit field is set by the base station toindicate the power control sub-channel number assigned to the mobilestation.

As described above with reference to the prior art CDMA systems, becausemobile stations transmit over a wide range of transmission power levels,it is advantageous to enable the base stations to supervise the mobilestations as soon as possible after the mobile stations attempt to accessthe system. By supervising the mobile stations as early as possible inthe channel assignment process, the base station limits the mobilestations' transmit power to levels that are sufficient to close thereverse link, but no greater. The potential interference that could becaused by a rogue mobile station transmitting at uncontrolled transmitpower levels is thereby reduced or eliminated.

In the CDMA system 100 designed for use with the present invention, apower control sub-channel is used by the base station to control thetransmit power of the mobile stations. The power control sub-channelcomprises information bits that are transmitted on the forward link. Thebase station continuously transmits “up/down” power control bits to themobile station based upon measurements of the reverse link signalquality. If the reverse link signal quality is above/below a targetthreshold, a “down”/“up” bit is sent and the mobile adjusts itstransmitter power a discrete amount in the direction indicated by thecontrol bit. Thus, the power control sub-channel is used to inform themobile station to either increase or decrease its transmitter power. Inthe system contemplated for use with the present invention, a limitednumber of power control sub-channel groups are available to the mobilestation. For example, in one exemplary system, only thirty-two powercontrol channels are available.

In order for the mobile station to begin transmitting data on thereverse link immediately after transmission of the access probe, themobile station must select one from among the available power controlgroups. In accordance with one embodiment of the present invention, thebase station advertises a range of available power control groups on theforward link. The mobile station randomly selects one of the availablepower control groups and requests the selected group in the accessprobe. Thereafter, the mobile station uses the selected power controlgroup to begin transmitting data on the reverse channel. As soon as themobile station selects a power control sub-channel, the base stationremoves the selected sub-channel from the available power controlsub-channel list. The time necessary to detect a power control groupselection and to remove the selected group from the available powercontrol sub-channel list is very short as compared to the mean timebetween call originations. Therefore, there is very little chance thattwo mobile stations will randomly select the same power controlsub-channel. However, should two mobile stations choose the same powercontrol bits, the call will terminate in a call set-up failure and themobile station will re-initiate the call processing sequence.

After the mobile station selects the power control sub-channel, the basestation associates the mobile's MSI with the selected power controlsub-channel. The MSI and power control sub-channel associations aresubsequently transmitted on the forward link to be verified by themobile station. The mobile station checks whether its MSI matches withthe power control sub-channel that it previously selected during thechannel assignment process. If a correct match is found, the mobilestation continues the call to exchange data with the base station.However, if an incorrect match is found, and the power controlsub-channel that it selected is erroneously associated with some otherMSI, the mobile station will terminate the call and attempt tore-initiate the call.

Thus, one advantage provided by the present invention is the ability ofa base station to immediately begin controlling the transmission powerof a mobile station once the mobile station accesses the CDMA system100. The mobile station is immediately transmitting on the trafficchannel identified by its MSI once it transmits its access probe. Thebase station thereby immediately supervises the mobile station as soonas the mobile station begins to transmit data over the traffic channel.

As described above, the present invention improves the traffic channelassignment process by allowing a mobile station to rapidly obtain atraffic channel after it transmits an access probe. The improvement inchannel assignment speed is partly due to the manner in which the packetdata CDMA system 100 manages the mobile station's MSI. Further, reverselink acquisition is not required using the present method and apparatus.

In contrast to the prior art approaches described above, the MSI used bythe present inventive method and apparatus is a randomly generatednumber that is assigned by the wireless packet data system to a mobilestation when the mobile station registers with the system and opens apoint-to-point connection. The MSI allows the system to differentiatebetween different users. The prior art systems base the PN sequences onthe mobile station's ESN. However, the MSI used by the present inventionallows the wireless packet data system to address a mobile stationwithout using its actual identification number (e.g., its ESN). Incontrast to the mobile station's ESN, the MSI is simply a temporaryidentifier used by the system to communicate with the mobile station. Inone embodiment, the MSI is randomly generated at the beginning of eachsession, and is de-assigned when the session terminates. In thisembodiment, an acceptably low collision rate results because the MSIcomprises a relatively large number (e.g., thirty-two bits). On the rareoccasions that a collision occurs (when two mobile stations are randomlyassigned an identical MSI), a call set-up failure occurs. However,because the MSI is a large number, the call set-up failure rate remainsacceptably low.

The MSI is used on the forward link to identify forward link trafficdata intended for a particular mobile station. Forward link data isprefaced with data preambles. Each preamble is covered with theappropriate MSI, and the covered data is transmitted over the forwardlink. The mobile stations monitor the forward channel looking for datathat is covered with its associated MSI. When a matching MSI is found,the mobile stations de-cover the associated data.

Another advantage provided by the present invention is an increase insystem capacity. Because the present invention speeds the channelassignment process, mobile stations can use the communication systemintermittently or for short duration service sessions as necessary toaccommodate short duration data transactions. Using the presentinvention, mobile stations can disconnect from or “tear down” theairlink whenever they are not sending data (e.g., when the mobilestations are in a dormant state). In contrast, in the prior art CDMAsystems, due to the overhead associated with the channel assignmentprocess, mobile stations are forced to maintain the airlink even whenthey are not exchanging data with the base station. By allowing themobile stations to release the airlinks more frequently, preciousresources can be freed and made available for other active mobilestations. Thus, system capacity is increased using the presentinvention. Both the mobile station and the base station can maintainstate on either side of the link, and tear down the airlink when thereis no further data to transmit. The present invention thus facilitatesshort duration data exchanges by speeding the channel assignmentprocess.

In accordance with the present invention, rather than requiring betweentwo and three seconds to acquire a traffic channel (as required in theprior art systems), a mobile station acquires a traffic channel withinthe time period defined by the probe tail 206 (FIG. 2). As describedabove with reference to FIG. 2, the base station advertises the probetail period via the forward link control channel. In one embodiment ofthe present invention, this time period comprises only a few shorttwenty-six millisecond intervals. For example, the probe tail 206 shownin FIG. 2 comprises four twenty-six-millisecond intervals, orapproximately 0.11 seconds. Thus, in the embodiment shown in FIG. 2, amobile station acquires a traffic channel in approximately one-tenth ofa second. This represents a tremendous channel assignment speedadvantage over the prior art techniques.

In addition, a power control sub-channel is assigned to a mobile stationin the same short time period. As described above, it is extremelyadvantageous to allow the base station to control the mobile station'stransmit power as early as possible in the channel assignment process.Using the inventive method described above with reference to FIG. 2, themobile station is supervised by the base station within approximately0.11 seconds after the access probe is transmitted. Once again, this isa vast improvement over the prior art techniques.

Advantageously, the present invention allows the base stations to usethe traffic channel, and not the control channel, for transmitting thetraffic channel assignment message to the requesting mobile station. Inthe system contemplated for use with the present invention, the trafficchannel operates at a far higher rate than does the control channel.Therefore, the traffic channel assignment message is transmitted to themobile station at a much higher rate than was previously available usingthe prior art systems i.e. a capacity advantage.

Base Station Advertisement of Available Traffic Channels

As described above, because the mobile station randomly selects thetraffic channel, and because the mobile station also randomly selects anavailable power control sub-channel, a relatively small chance ofcollision exists. That is, there is a relatively small chance that morethan one mobile station will randomly select either the same trafficchannel or the same power control sub-channel. However, in cases wherecollisions cannot be tolerated by the wireless communication system, analternative embodiment of the present invention is available thatreduces the randomness of the channel selection process, and therebyreduces or eliminates the collision rate. In accordance with thisalternative embodiment, a base station uses the control channel toadvertise the identity of available traffic channels.

In accordance with this embodiment, the available traffic channels areadvertised on the control channel as channel identifier and associatedpower control sub-channel couples or pairs. For example, in oneembodiment, the base station transmits a plurality of available channelpairs defined as (Wi, Pi), where Wi represents the identity of anavailable traffic channel, and Pi represents the identity of itsassociated power control sub-channel. The traffic channel request andassignment process is similar to that described above with reference toFIG. 2, except that, instead of randomly selecting a traffic channelbased on its MSI, the mobile station selects a channel pair from theavailable channel list advertised by the base station. The base stationdetects the selection and removes the selected pair from the availablechannel list.

After choosing an available channel pair (Wi, Pi), the mobile stationtransmits an access probe on the access channel in the manner describedabove with reference to FIG. 2. The base station determines whether morethan one mobile station requested the same traffic channel pair. If morethan one mobile station attempted to use the same traffic channel pair,the base station releases one or more mobile stations that thenre-initiate calls. The remainder of the channel assignment processproceeds as described above with reference to FIG. 2.

This alternative embodiment reduces the potential collisions that mayoccur using a totally random channel (and power control sub-channel)selection process. In accordance with this embodiment, the mobilestation is assigned a power control sub-channel (defined by Pi) that isavailable from the moment the mobile station begins using the trafficchannel. Thus, the base station can immediately supervise the mobilestation (i.e., control its transmission power) using the selected powercontrol sub-channel as soon as it receives the traffic channel request.As described above, there is a chance that more than one mobile stationwill select the same power control sub-channel from those that areavailable (i.e. that a collision will occur). However, because the basestation detects the selection and removes the selected pair from theadvertised list in a very short time frame compared to the timenecessary to initiate a call, the chance of collision is very small.However, in case of collision, the call will terminate in a call set-upfailure. Because collisions occur only very rarely, the call set-upfailure rate is acceptably low using the present invention. For example,using this embodiment of the present invention, collisions will occuronly when equidistant mobile stations simultaneously select the sameavailable traffic channel pair (Wi, Pi). Effectively, this embodimentadvantageously creates multiple access channels that can carry trafficchannel request messages.

Base Station Initiated Traffic Channel Assignment

In an alternative embodiment of the present method and apparatus, thebase station, and not the mobile station, initiates data calls andsubsequent traffic channel assignments. This case occurs when data ispresented to a base station that requires transmission to a particularmobile station (e.g., an Internet provider sends data associated with aparticular mobile station). In accordance with this embodiment, whenevera base station is presented with data for transmission to a mobilestation that is not currently connected to the base station (i.e., themobile station is in an “idle” state), the base station initiates thetraffic channel assignment process. When data is to be transmitted to aparticular mobile station, a base station controller directs all basestations within the mobile station's paging radius (i.e., where themobile station is most likely to be presently located) to send “page”messages on the forward link control channel. The page messagesadvertise the mobile station's identity using the mobile station's MSI.The page messages are sent in an initial transmission on the controlchannel (referred to as a “capsule”). The mobile station continuouslymonitors the control channel and responds to pages addressed to itsassociated MSI. Once the mobile station receives its page message, itpreferably uses either of the two inventive traffic channel assignmentmethods described above to initiate a traffic channel request.

Fast Base Station Initiated Traffic Channel Assignment

In another alternative embodiment of the present method and apparatus,the base station initiates a traffic channel assignment by advertisingboth the identities of a destination mobile station (using the mobilestation's MSI as an identifier) and an associated power controlsub-channel over the control channel. As described above, the basestation initiates a traffic channel assignment whenever data ispresented to a base station requiring transmission to a particularmobile station. Similarly to the alternative embodiment described above,all base stations within the paging radius of the destination mobilestation transmit a page message to the mobile station via the controlchannel. However, in accordance with this alternative embodiment, thebase station not only advertises the mobile station's MSI in a controlchannel page message, but it also advertises an associated power controlsub-channel. The mobile station continuously monitors the forward linkcontrol channel and subsequently identifies the page message associatedwith its MSI.

When the mobile station detects its page message and its associatedpower control sub-channel, it transmits a traffic channel request (in amanner described above with reference the inventive traffic channelassignment method and apparatus) to the base station on the reverse linktraffic channel defined by its MSI. The mobile station immediatelybegins monitoring the forward link power control sub-channel defined inthe page message. Advantageously, the base station may immediately beginusing the assigned power control sub-channel to control the transmissionpower of the selected mobile station.

The rapid channel assignment method of the present invention preferablyexecutes on microprocessors 150. 152, 154 or other data processingdevices in both the mobile station and the base station. The mobilestation cooperates with the base station as described above to rapidlyand efficiently request and assign traffic channels in a wireless packetcommunication system. The method and apparatus of the present inventioncan alternatively be implemented using any convenient or desirablesequencing devices such as state machines, present state-next statediscrete logic, or field programmable gate array devices. The rapidchannel assignment methods described above can be implemented inhardware (i.e., “hardwired”) or alternatively can be implemented usingprogrammable devices.

In summary, the method and apparatus includes a means for rapidlyassigning traffic channels to requesting mobile stations in a wirelesshigh-speed packet data communication system. The present method andapparatus allows a mobile station to begin using a selected reversetraffic channel immediately or soon after transmitting a traffic channelrequest to a selected base station. In accordance with the presentinvention, a mobile station sends an access probe on a randomly selectedaccess channel to the selected base station. The access probe comprisesa pilot preamble, a traffic channel request, and a pilot/DRC field. Thepilot preamble allows the base station to easily detect the access probetransmission from the mobile station. The traffic channel requestincludes data that identifies the mobile station to the base station.The mobile station continues to transmit the pilot/DRC field for aperiod defined by a probe tail parameter advertised by the base station.Advantageously, the mobile station is assigned a traffic channel in avery short time period as compared with prior art assignment techniques.In addition, the mobile station is assigned a power control sub-channelalmost immediately.

The present invention advantageously reduces the time delays heretoforeassociated with the traffic channel request and assignment process. Thepresent invention improves system capacity, frees valuable systemresources, enables early power supervision of mobile stations, andfacilitates use of short duration data transactions in a wireless packetdata cellular communication system. By reducing the amount timeassociated with the call setup process, the present invention reducesthe system costs associated with dormant mobile stations. The presentinvention is particularly useful in a cellular/PCS CDMA system thatprovides wide-area high-speed packet data connectivity for both fixedand mobile terminals. However, it also finds utility in any broadbandwireless data communication system that requires rapid assignment oftraffic channels to mobile stations.

A number of embodiments of the present invention have been described.Nevertheless, it will be understood that various modifications may bemade without departing from the spirit and scope of the invention. Forexample, although one embodiment of the access probe is shown in FIG. 2,the present invention can utilize a wide variety of access probeformats. For example, the duration of the pilot preamble, trafficchannel request, and pilot/DRC field can vary from the duration shown inFIG. 2. The mobile station can transmit a pilot preamble for a durationthat exceeds the twenty-six-millisecond frame shown in FIG. 2.Similarly, in an alternative embodiment, the traffic channel request canbe transmitted after the transmission of some other reverse link data.Additionally, the present invention may use a variety ofsystem-generated parameters to identify mobile stations. For example,the present invention may alternatively use mobile station serialnumbers, universal mobile station names similar to the well-knownInternet domain names, a hash function of the universal mobile stationnames and universal mobile station identifiers similar to those used inIS-95.

Accordingly, it is to be understood that the invention is not to belimited by the specific illustrated embodiment, but only by the scope ofthe appended claims.

1. A mobile station operable to communicate wirelessly with a basestation, the mobile station comprising: a processor configured to selectan access channel; and a mobile termination block configured to (a)transmit a pilot preamble and a traffic channel request to a basestation on the selected access channel, the traffic channel requestcomprising a mobile station identifier, and (b) transmit data on atraffic channel identified by the mobile station identifier to the basestation without waiting to receive a traffic channel assignment from thebase station.
 2. The mobile station of claim 1,wherein the processor isfurther configured to (a) determine which base station is sending apilot signal which is stronger than any other pilot signal received bythe mobile station and (b) select an access channel to send the a pilotpreamble and traffic channel request to the determined base station. 3.The mobile station of claim 1, wherein the processor is configured torandomly select the access channel from a plurality of access channels.4. The mobile station of claim 1, wherein the processor is configured toselect the access channel from a list of access channels advertised bythe base station.
 5. The mobile station of claim 1, wherein the pilotpreamble and traffic channel request are masked with a long code accesschannel cover.
 6. The mobile station of claim 1, wherein the pilotpreamble comprises a sequence of data that is detectable by the basestation.
 7. The mobile station of claim 1, wherein the mobile station isconfigured to register with a wireless system comprising the basestation, the wireless system assigning the mobile station identifier andsending the mobile station identifier to the mobile station.
 8. Themobile station of claim 1, Wherein the traffic channel request furthercomprises a transaction identifier, a reference pilot, a pilot strengthindicator, and a timer status field.
 9. The mobile station of claim 1,wherein the traffic channel request further comprises signal strengthsand identities of all base stations having received signal strengthsexceeding a threshold.
 10. The mobile station of claim 1, wherein themobile termination block is further configured to transmit a datarequest channel (DRC) on the traffic channel after transmitting thepilot preamble and traffic channel request on the access channel. 11.The mobile station of claim 10, wherein the data request channel (DRC)is masked with a long code comprising a mobile station identifier (MSI)cover.
 12. The mobile station of claim 10, wherein the DRC comprisestraffic channel data rate information usable by the mobile station torequest a maximum data rate from the base station with which the mobilestation can reliably demodulate data.
 13. The mobile station of claim10, wherein the mobile station is configured to continue transmittingthe DRC for a pre-defined time period.
 14. The mobile station of claim1, wherein the mobile termination block is further configured totransmit pilot channel information on the traffic channel aftertransmitting the pilot preamble and traffic channel request on theaccess channel.
 15. The mobile station of claim 14,wherein the pilotchannel information is masked with a long code comprising a mobilestation identifier (MSI) cover.
 16. The mobile station of claim 1,further comprising a receiver configured to receive a traffic channelassignment message transmitted by the base station.
 17. The mobilestation of claim 1, wherein the mobile termination block is configuredto use Code Division Multiple Access (CDMA) to process data fortransmission to the base station.
 18. The mobile station of claim 1,wherein the mobile termination block is configured to transmit asequence of pilot preambles and traffic channel requests with increasingpower until the traffic channel request is acknowledged by the basestation or the sequence ends.
 19. The mobile station of claim 1, whereinthe processor is further configured to select a power control group froma plurality of power control groups for the mobile termination block totransmit data.
 20. An apparatus comprising a mobile termination blockconfigured to receive page messages via a control channel sent by atleast one base station; and a processor configured to (a) determinewhether one of the page messages is addressed to the apparatus, (b)select a reverse link access channel to transmit a traffic channelrequest whenever the processor determines a page message is addressed tothe apparatus, wherein the mobile termination block is configured totransmit the traffic channel request to a base station using theselected reverse link access channel and transmit data on a trafficchannel identified by a mobile station identifier before receiving achannel assignment from the base station.
 21. The apparatus of claim 20,wherein the mobile termination block further transmits a pilot preamblealong with The traffic channel request to a base. station using theselected reverse link access channel.
 22. The apparatus of claim 20,wherein the data transmitted on a traffic channel identified by a mobilestation identifier comprises a data request channel (DRC) field.
 23. Theapparatus of claim 20, wherein the processor selects one of a group ofadvertised available power control sub-channels for communicating withthe base station.
 24. The apparatus of claim 20, wherein the processorselects a traffic channel from list of advertised available trafficchannels and associated available power control sub-channels forcommunicating with the base station.
 25. A mobile station operable tocommunicate wirelessly with a base station, the mobile stationcomprising: means for selecting an access channel; and means for (a)transmitting a pilot preamble and a traffic channel request to a basestation on the selected access channel, the traffic channel requestcomprising a mobile station identifier, and (b) transmitting data on atraffic channel identified by the mobile station identifier to the basestation without waiting to receive a traffic channel assignment from thebase station.